1. Field of the Invention
The present invention relates to a display device and a touch sensing method thereof, and more particularly, to a display device with integrated touch sensor and a touch sensing method thereof.
2. Discussion of the Related Art
With the advancement of various portable electronic devices such as mobile terminals and notebook computers, the demand for flat panel display devices applied to the portable electronic devices is increasing.
Liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission display (FED) devices, light emitting diode (LED) display devices, and organic light emitting diode (OLED) display devices have been developed as flat panel display devices.
In such flat panel display devices, LCD devices are easily manufactured by advanced manufacturing technology and have drivability of drivers, low power consumption, high image quality, and a large screen, and thus, the application fields of the LCD devices are being expanded. LCD devices, including a built-in touch screen that enables a user to directly input information to a screen with a finger or a pen, are attracting much attention.
In applying a touch screen to LCD devices, a separately prepared touch panel is conventionally disposed on a liquid crystal panel, but, liquid crystal panels with a built-in touch screen are developed for slimming.
Especially, LCD devices using the existing elements, such as common electrodes formed in a lower substrate, as touch sensing electrodes are called in-cell touch LCD devices.
In in-cell touch LCD devices, a liquid crystal panel for displaying an image display and a touch screen for sensing a user's touch are temporally divided and driven (time-divisional driven) due to a structural characteristic in which a plurality of pixels for the liquid crystal panel and the touch screen (that the liquid crystal panel in which a plurality of pixels for an image display are disposed and the touch screen in which a plurality of touch driving electrodes and touch sensing electrodes are arranged) are provided together.
During a touch sensing period (non-display period), when a capacitance is changed in a touch sensing block touched by a user's finger (due to a touch by a user's finger), a touch sensing electrode senses (the touch sensing electrodes sense) the capacitance change, thereby determining whether there is the user's touch and a position touched by the user.
In the related art, however, when touch sensors (sensing electrodes) are disposed outside a liquid crystal panel, an image display function and a touch sensing function are separately performed, and thus no interferer between the two functions can occur. On the other hand, when the touch sensors (sensing electrodes) are built in the liquid crystal panel, the image display function and the touch sensing function may interfere with each other.
That is, touch sensing driving can affect display driving, or vice versa, the display driving can affect the touch sensing driving. This will now be described in more detail with reference to FIG. 1.
FIG. 1 is a view showing a capacitance change in a pixel displaying black and a capacitance change in a pixel displaying white, in a related art in-cell touch type LCD device.
As seen in FIG. 1, a pixel “Black” displaying black and a pixel “White” displaying white differ in alignment of liquid crystal, and thus, a difference “Cm_w−Cm_b” between capacitances of a liquid crystal layer occurs.
The capacitance difference between pixels is maintained in the pixels even after a touch sensing period is started, and thus affects touch sensitivity. The capacitance difference functioning like offset to act as noise to touch sensing is called display touch crosstalk.
The display touch crosstalk reduces the accuracy and stability of touch.